21985821 has 36 divisors (see below), whose sum is σ = 37616124. Its totient is φ = 12291840.

The previous prime is 21985783. The next prime is 21985823. The reversal of 21985821 is 12858912.

It can be written as a sum of positive squares in 2 ways, for example, as 2722500 + 19263321 = 1650^2 + 4389^2 .

It is not a de Polignac number, because 21985821 - 2⁶ = 21985757 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21985823) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 13381 + ... + 14933.

Almost surely, 2^21985821 is an apocalyptic number.

It is an amenable number.

21985821 is a deficient number, since it is larger than the sum of its proper divisors (15630303).

21985821 is a wasteful number, since it uses less digits than its factorization.

21985821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1594 (or 1580 counting only the distinct ones).

The product of its digits is 11520, while the sum is 36.

The square root of 21985821 is about 4688.9040297281. The cubic root of 21985821 is about 280.1437229836.

The spelling of 21985821 in words is "twenty-one million, nine hundred eighty-five thousand, eight hundred twenty-one".